1. Field of the Invention
This invention relates to a dispensing apparatus, and in particular to a dispensing apparatus for dispensing viscous material.
2. Discussion of Background Information
Mastics are now being increasingly used as a sealant, filler and adhesive. A typical mastic is a soft putty-like substance which is conveniently contained in a generally cylindrical cartridge from which the mastic can be forced out in a convenient measure for the application at hand. The type of mastic is generally engineered to a particular use, but in many applications this can lead to problems since the eventual viscosity may be such that the mastic is difficult to force out of the cartridge without the use of a special device known as a gun. In fact, the use of a gun is preferred since this can make it simpler to discharge a specific or controlled amount of the mastic in a repeatable manner.
Some mastics also require the use of a catalytic hardener which must be mixed with the mastic. The hardener can either be added after dispensing of the mastic or a hardener cartridge can be incorporated with the gun. In the automotive after market field, for example, use of the correct proportions of mastic to hardener helps solve problems which might arise from the paint formulations applied to modern vehicles. Thus, it is quite common for garages to employ a movable or permanently mounted dispensing gun for dispensing correct proportions of the mastic and hardener.
With the advent of specialized mastics for different applications, it is now common to use more than one type of mastic in a garage, thus requiring either continual changing of the mastic and hardener loaded in the gun or the expense of a number of guns containing different types of mastics.
A known dispensing apparatus or gun for dispensing viscous material that is quite simple and encompasses the common concepts of the prior art is described in UK-A1,555,455. The mastic containing cartridge for such a gun comprises a cylindrical casing full of mastic which has an exit nozzle opening at one end and is closed at the other end by a plate which, provided the casing is fixedly held, can slide along the axis of the casing thereby compressing the mastic and forcing it out of the nozzle.
The gun itself comprises a single plate stock which is stamped to form bridges for guiding and holding a central drive rod which acts on the aforementioned plate of a received cartridge held by the gun. The holder for the cartridge comprises two metal strips which are welded to extend in opposing manner from the stock and have a 90 degree twist adjacent the stock. The end of the strips remote from the stock are welded to a cup-shaped member having a large opening in its base. The cartridge is inserted into the holder between the strips with the plate end of the cartridge being seated against the stock and with the exit nozzle located in the cup-shaped member. A drive rod gripper, gun trigger and gun butt are provided respectively for advancing the drive rod, actuating the advance thereof and for holding the gun.
Where a hardener is required, the gun incorporates a further mounting arrangement for a hardener cartridge having a similar construction to that of the mastic containing cartridge. A secondary rod is provided to force out the hardener at the same time as the mastic. This makes for a relatively expensive piece of equipment for the simple task of dispensing mastic and hardener.
The setting time of the mastic/hardener mix is typically of the order of 15 to 30 minutes. Generally, such a gun is used a number of times during a day, but even then, the mastic and hardener cartridge is often not emptied for some time. Thus, the gun is used repetitively rather than a single shot.
Unfortunately, during use, there often occurs cross-contamination between the hardener and mastic cartridges thus leading to the appearance of small solid bits in later mixes from the gun or even blockage of the cartridges themselves. Moreover, as the gun is repeatedly used, spillage occurs so that set mastic gradually builds up on the gun forcing its eventual replacement.